1. Field of the Invention
The present invention relates to pulse modulators. More specifically, the invention pertains to a pulse modulator for conversion of a complex input signal to a pulsed signal, and to a method for pulse modulation of a complex input signal.
2. Description of the Prior Art
Digital/analog converters may be employed to convert digital input signals to analog signals. They are, however, expensive and require a relatively large amount of electrical power as well as a number of supply voltages (frequently). They are also difficult to integrate with digital electronics and, thus, limit miniaturization.
As a result, digital/analog converters are being replaced by digital pulse modulators (e.g., sigma-delta converters) in many applications. A conventional sigma-delta modulator includes an integrator that integrates the difference signal between an input signal and a fed-back quantized signal, as well as a quantizer that quantizes the integrated signal. A quantized pulsed signal can then be tapped off at the output of the quantizer. It is fed back as a feedback signal to the input of the sigma-delta converter. Sigma-delta modulators are distinguished by a noise characteristic in which the quantization noise is shifted from the low-frequency range in the vicinity of ω=0 towards higher frequencies. The noise that occurs at higher frequencies can then be suppressed with the aid of a downstream low-pass filter. Sigma-delta converters can be implemented at low cost and integrated with digital electronics. However, for some applications, it would be advantageous to be able to keep the quantization noise low at higher frequencies.